The present invention is in the field of manholes and is particularly directed to a novel and unique means for providing invert channels in the base of a manhole assembly through a two pour fabrication method which permits the obtainment of accurately positioned and aligned inverts for any type of flow system including plural inverts and junctures of different sized inverts flowing from pipes and oriented at different angles of inclination.
Conventional systems employed for handling sewage, storm drainage and the like employ vertically oriented manholes of generally cylindrical shape which are positioned at juncture locations of diverse flow pipes which discharge into the manhole with the manhole being provided with trough-like conduits referred to as inverts in its lower end portion. The inverts insure that the inwardly flowing material is directed into an outflow channel for subsequent movement downstream from the manhole. Inflow pipes frequently arrive at the manhole location at different elevations and are frequently of different sizes so that the formation of the necessary inverts is a complex and challenging endeavor.
Invert channels are frequently installed at the job site by hand forming and pouring, an operation which does not insure consistent uniformity, strength and appearance. Moreover, the field conditions under which such hand forming and pouring are performed are frequently adverse both from a technical sense and an economic sense. For example, it is essential that an adequate amount of mixed concrete be available at the job site in order for the invert channels to be properly formed. It is also obviously desirable that expensive concrete not be wasted and any miscalculation in the amount of concrete ordered which results in either a shortage or overage of concrete obviously increases the cost of the job. Moreover, the hand forming of invert channels requires skilled and expensive labor which is frequently difficult to obtain. Consequently, a number of devices have been proposed for the purpose of reducing the cost of providing manholes with invert channels and a number of such devices have been the subject of United States patents. The most relevant prior patents of which we are aware of U.S. Pat. Nos. 725,098; 1,145,228; 1,560,811; 3,363,876; 4,085,918; 4,103,862; 4,119,291; 4,177,229; 4,276,245; 4,278,229; 4,318,880; 4,422,994; 4,484,724; 4,565,347 and 4,566,483. Many of the prior art devices recognize the desirability of prefabricating manholes including inverts in a factory and while a number of the above patents represent a definite improvement over prior known hand forming techniques, they still suffer from a number of shortcomings including an inability to accommodate different sizes of invert channels, an inability to provide invert channels at different angles and inclinations. Some of the prior art devices are overly complex and difficult to use. Others are easily susceptible to damage and wear and must be frequently repaired or replaced. Others, such as U.S. Pat. No. 4,484,724 require additional bracing (i.e. means 56,62) to hold the invert molds in position against the buoyant forces of the wet concrete.
Factory construction of manholes is now widely employed with two types of systems being used. The first system, frequently referred to as a two-pour operation, involves a first pour of concrete for effecting the molding of the cylindrical side wall and a bottom wall, base or floor portion of a manhole with openings being provided in the side walls for connection to pipe members when the manhole is installed in the field. After the manhole wall and base construction has been cured, the inverts are molded in the lower portion of the cylindrical wall on the base portion by the positioning of U-shaped molding members extending across the width of the base of the system in the orientation required for the particular inflow openings of the particular manhole. A second pour of concrete is then poured into the bottom end of the manhole and is filled upwardly to a level generally adjacent the upper edges of the U-shaped molding members. A process of the aforementioned type is disclosed in U.S. Pat. No. 4,484,724. When the second pour of concrete has set, the invert channel forming molding members are removed to complete the manhole construction.
A second type of construction referred as a single-pour construction is also employed in a manhole factory. In the single-pour construction the manhole is cast in mold means which is in an inverted orientation as compared to the final manhole product in which the top of the mold member is provided with upward protrusions which define the invert to be formed in the manhole base. The mold includes concentric side walls which extend downwardly from the top of the mold member to define a cylindrical space which is filled with concrete which will eventually define the outer cylindrical wall of the manhole. Techniques for such single pour manhole forming operations are disclosed in U.S. Pat. Nos. 3,363,876; 4,103,862; 4,177,229; 4,422,994; and 4,565,347.
Therefore, it is the primary object of the present invention to provide a new and improved invert channel forming system.
A further object of the present invention is the provision of a new and improved invert channel forming system that is reliable, rugged and easy to use.
Yet another object of the present invention is the provision of a new and improved invert channel forming means that is versatile and can be used for forming invert channels of various sizes, shapes and angles of inclination.
Another object of the invention is the provision of an improved invert channel forming mold means not requiring the use of supplemental bracing for holding it in position.